Arthroscopy is becoming a popular method for removing diseased or damaged tissue from intra-articular regions of the body. Basically, arthroscopy is a method of surgery involving the use of probes for viewing and operating on regions of the body such as knee joints and other intra-articular regions. Its benefits arise from the smaller incisions involved which cause less scarring and heal more quickly than larger incisions required for other surgical techniques.
A variety of cutting devices have been developed for arthroscopy which include an outer tube sized and shaped for insertion through a puncture in the flesh with an inner tube adapted to rotate relative to the outer tube. These cutting devices typically have a side-facing opening through the inner and outer tubes into which tissue is drawn by a partial vacuum in the inner tube. As the inner tube rotates relative to the outer tube, the tissue drawn into the opening by the vacuum is cut off by the cutting interaction of the edges along the openings or of blades otherwise located in the instrument. This type of device is shown generally in U.S. Pat. Nos. 4,210,146; 4,203,444; 4,167,944; 3,996,935; 3,945,375; 3,844,272; and 3,618,611.
As surgeons gained greater experience with these devices, it became apparent that they operated better at higher rotating speeds. It was found that tissues tended to be cut in smaller pieces and less tearing of the tissues occurred at higher RPM's. At these higher operational speeds, bearings or other means for maintaining the alignment of the inner cutting member relative to the outer tube became increasingly more important.
Attempts to develop devices with improved alignment are described in several U.S. patents. For example, U.S. Pat. No. 4,203,444 shows radial bearing surfaces 33, 35 on each side of the cutting blade at the side-facing window at FIG. 4 and a ring 37 at FIG. 3 for journaling the inner tube within the outer tube. U.S. Pat. No. 3,996,935 shows a conical inner seat 75 at the end of the outer tube with the tip of the conical seat pointing outwardly at the axial centerline of the tube and a corresponding end portion on the inner cutting member with a conical exterior surface 78 at FIG. 7. U.S. Pat. No. 3,844,272, by the same inventor as U.S. Pat. No. 3,996,935, shows a similar conical seat arrangement at FIG. 18A. This arrangement requires that the cutting opening be located at a relatively great distance from the tip because of the length of the solid bar necessary to form the bearing, causing unnecessary tissue disturbance.
None of these devices is believed to have a satisfactory bearing arrangement for maintaining proper axial alignment during operations at higher speeds and under non-axial loading conditions.